Here's a revised mockup, with some tentative ideas of animals.
The thing about the fish and the duck is that they're both identifiable as 2 color silhouttes, so did some thinking about animals with simple, interesting body forms and iconic colors. I think an overhead view of a bee with the nice striped tail-end (form and colors) and a jumping frog from either a top or side view (mainly form) would be identifiable and have some character.
I'm still not happy with the buffalo, but I'm not sure what kind of mammal would fit this kind of thinking. I think the tiger suggestion may be too complicated to convey, and, given how all these other animals are turning out to be tiny little buggers, a little unbalancing (which is another reason I'm getting unsatisfied with the bison).